Watchdog group: Cain campaign broke campaign-finance laws

In a legal complaint filed today, a public watchdog group charged that Herman Cain's top campaign aide illegally used corporate funds to pay for iPads and charter flights for Cain's fledgling presidential campaign.

The charges are based on documents -- first disclosed this week by the Milwaukee Journal Sentinel -- showing that funds from a non-profit founded by Cain campaign Chief of Staff Mark Block (called Prosperity USA) were used to pay early expenses for Cain's presidential campaign.

Non-profit groups are barred by law from contributing to political campaigns.

The Cain campaign has said it has retained an outside counsel to investigate the allegations. Cain's campaign lawyer told NBC this week, "We take these allegations very seriously," but declined further comment or to identify the outside counsel.

The complaint alleging election law violations was filed with the Federal Election Commission by the Citizens for Responsibility and Ethics (CREW) in Washington. Melanie Sloan, the group's executive director, said:

"As hard as Mr. Cain is trying to prove himself a different kind of candidate, he still has to play by the same rules as everyone else. It is not sufficient for the Cain campaign to investigate itself. Rather, the FEC-- the federal agency charged with enforcing campaign finance laws -- must look into the matter."

Non-profit groups like Prosperity USA are not required to disclose their donors. But Americans for Prosperity, the conservative advocacy group for whom Block once worked, said Thursday it is reviewing "financial dealings" it had with Prosperity USA.

Americans for Prosperity -- at whose annual meeting Cain is speaking today -- also does not disclose its donors. It was founded by David and Charles Koch, of Koch Industries, and it's closely affiliated with the Tea Party.